High power limiters are used to prevent damage to devices such as a low noise amplifier. In one example implementation, a radio frequency receiver include a power limiter in combination with a low noise amplifier. The power limiter limits power provided to the low noise amplifier to avoid damage to the low noise amplifier. Such damage may occur where a receiver is configured to detect low amplitude radio frequency signals and it instead receives a high amplitude signal. Example limiters include reflective limiters and absorptive limiters.
Reflective limiters generally involve shunting PIN diodes to ground in parallel with an RF choke. Alternatively, PIN diodes are shunted to ground in parallel with NIP diodes. Thus, for low radio frequency levels the PIN diode is off and no current flows to ground; the limiter has low loss. For high voltage swings, however, the PIN diode turns on and current flows to ground. Either the choke or the NIP diode provides a current path. In such a case, the received signal is reflected toward the signal source. This results in a disadvantage in that, for example, a clandestine radio frequency receiver can be seen when it reflects the radio frequency energy back to its source.
Absorptive limiters generally use a quarter wave shunt with PIN diodes. For low amplitude received signals the PIN diodes are off, resulting in low current flow. Thus the limiter has a low loss. For high levels, however, the PIN diodes turn off and current flows. In such a case, the output diodes look like a low impedance when turned on. The low impedance of the output diode reflects through a quarter wave line and looks like an open circuit in parallel with a 50 ohm load. Thus, the radio frequency energy is absorbed by the 50 ohm load.
The above-described reflective and absorptive limiters are not satisfactory in all regards. In particular, in certain applications the limiters do not act sufficiently to limit received power.